It happened on Thursday, March 8th at 5:20 a.m.
Police say the 25-year-old woman entered the 135 Street Subway Station at 137th Street and St. Nicholas Avenue.
As she went through the turnstile the suspect ran up to the victim, grabbed her and sexually assaulted her.
The suspect then fled the location on foot.
The victim later went to an area hospital where she was treated for her injuries.
The suspect is described as a light skinned male black, approximately 20 to 25 years old.
He is approximately 5'9, with a thin build.
He was last seen wearing a red hooded sweatshirt with white lettering in the front.
Anyone with information in regards to this incident is asked to call Crime Stoppers at 1-800-577-TIPS (8477).
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